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This Week in Science: Mar 15, 2019

In Science this week, an international research team reports an analysis of ancient DNA recovered from more than 200 Iberians — including 176 from a largely unsampled period after 2,000 BC — yielding a high-resolution time transect of the Iberian Peninsula. The reserachers identify high genetic substructure between northwestern and southeastern hunter-gatherers before the spread of farming. They also find evidence of sporadic contacts between Iberia and North Africa by around 2,500 BC until the replacement of 40 percent of Iberia's ancestry and nearly all of its Y-chromosomes by people with Steppe ancestry 500 years later. Other findings include the spread of Steppe ancestry into into both Indo-European–speaking and non-Indo-European–speaking regions in the Iron Age. By the Roman Age, the team writes, the ancestry of the peninsula was transformed by gene flow from North Africa and the eastern Mediterranean. GenomeWeb has more on this and a related study, here.

Also in Science, a group of French and UK investigators present new insights into the reproductive strategy of Mesorhabditis belari — a nematode species that produces only 9 percent males. M. belari females are known to use the sperm of males, usually from another species, to activate their oocytes, but do not use sperm DNA, resulting in only female offspring. The scientists discovered, however, that sperm DNA is used in about 9 percent of cases, producing only sons because the Y-bearing sperm of males are much more competent than the X-bearing sperm for penetrating the eggs. "In this previously unrecognized strategy, asexual females produce few sexual males whose genes never re-enter the female pool," they write. "Here, production of males is of interest only if sons are more likely to mate with their sisters. … In this context, the production of 9 percent males by M. belari females is an evolutionary stable strategy."